1. Field of the Invention
The present invention relates to a power modulator provided with a transformer used in particular to supply electromagnetic energy to resonant cavities of a linear accelerator.
In a linear accelerator, electrons emitted by a gun pass through a series of electromagnetic cavities. During their passage in these cavities, they are accelerated by the electromagnetic field that exists therein. At the output of this series of cavities these electrons hit a target at great speed which in turn emits other particles. These latter particles are thus used in industrial irradiation applications or in radiotherapy applications according to known methods. The main characteristic of these latter particles is their energy bound to the energy of the incident electrons.
To confer great energy on the incident electrons, it is necessary that the electromagnetic field prevailing in the cavities be dense. For both techological and utilization reasons, the operating of a linear accelerator is of the impulse type. This means that the electromagnetic field is established in the cavities for short durations, for example, from several nanoseconds to several hundred microseconds and with a certain periodicity, for example, from 25 to 1000 Hertz.
The establishment of the electromagnetic field in the cavities is obtained through inductive or capacitive coupling of these cavities to an electronic tube. For operating frequencies lower than several hundred Megahertz, the electronic tube utilized is generally a triode. By operation, upon the appearance of a very high direct current voltage between the cathode and the anode of this tube, is emitted an electromagnetic field between its electrodes. The oscillation frequency of this field is imposed by the forms and dimensions of the cavities.
2. Description of the Prior Art
In the prior art techniques the very high voltage applied between the cathode and the anode of the triode tube, currently in the range of several score kilovolts, is obtained by raising, by an impulse transformer having a transformation ratio (equal to N.sub.2 /N.sub.1) lower than 20, the voltage of impulsions produced by a high voltage stage. The high voltage stage must therefore supply impulses with an amplitude higher than several thousand volts. The realization of this high voltage stage is expensive.